Method and apparatus for photomask plasma etching

ABSTRACT

A method and apparatus for etching photomasks is provided herein. In one embodiment, the apparatus comprises a process chamber having a support pedestal adapted for receiving a photomask. An ion-neutral shield is disposed above the pedestal and a deflector plate assembly is provided above the ion-neutral shield. The deflector plate assembly defines a gas flow direction for process gases towards the ion-neutral shield, while the ion-neutral shield is used to establish a desired distribution of ion and neutral species in a plasma for etching the photomask.

CROSS-REFERENCE TO RELATED APPLICATIONS

The subject matter of this application is related to the subject matterdisclosed in U.S. patent application Ser. No. 10/880,754, entitled“METHOD AND APAPRATUS FOR QUASI-REMOTE PLASMA ETCHING”, filed on Jun.30, 2004, by Todorow, et al., and in U.S. patent application Ser. No.10/882,084, entitled “METHOD AND APAPRATUS FOR PHOTOMASK PLASMAETCHING”, filed on Jun. 30, 2004, by Kumar, et al., and in U.S. patentapplication Ser. No. 11/554,495, entitled “METHOD AND APAPRATUS FORPHOTOMASK PLASMA ETCHING”, filed concurrently herewith, by Kumar, etal., all of which are hereby incorporated herein by reference in itsentirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Embodiments of the present invention generally relate to a method andapparatus for plasma etching photomasks and, more specifically, to amethod and apparatus with improved control of distribution of plasmaspecies.

2. Description of the Related Art

The fabrication of microelectronics or integrated circuit devicestypically involves a complicated process sequence requiring hundreds ofindividual steps performed on semiconductive, dielectric and conductivesubstrates. Examples of these process steps include oxidation,diffusion, ion implantation, thin film deposition, cleaning, etching andlithography. Using lithography and etching (often referred to as patterntransfer steps), a desired pattern is first transferred to aphotosensitive material layer, e.g., a photoresist, and then to theunderlying material layer during subsequent etching. In the lithographicstep, a blanket photoresist layer is exposed to a radiation sourcethrough a reticle or photomask containing a pattern so that an image ofthe pattern is formed in the photoresist. By developing the photoresistin a suitable chemical solution, portions of the photoresist areremoved, thus resulting in a patterned photoresist layer. With thisphotoresist pattern acting as a mask, the underlying material layer isexposed to a reactive environment, e.g., using wet or dry etching, whichresults in the pattern being transferred to the underlying materiallayer.

The pattern on a photomask, which is typically formed in ametal-containing layer supported on a glass or quartz substrate, is alsogenerated by etching through a photoresist pattern. In this case,however, the photoresist pattern is created by a direct write technique,e.g., with an electron beam or other suitable radiation beam, as opposedto exposing the photoresist through a reticle. With the patternedphotoresist as a mask, the pattern can be transferred to the underlyingmetal-containing layer using plasma etching. An example of acommercially available photomask etch equipment suitable for use inadvanced device fabrication is the Tetra™ Photomask Etch System,available from Applied Materials, Inc., of Santa Clara, Calif. The terms“mask”, “photomask” or “reticle” will be used interchangeably to denotegenerally a substrate containing a pattern.

With ever-decreasing device dimensions, the design and fabrication ofphotomasks for advanced technology becomes increasingly complex, andcontrol of critical dimensions and process uniformity becomesincreasingly more important. Therefore, there is an ongoing need forimproved process monitor and control in photomask fabrication.

SUMMARY OF THE INVENTION

The present invention generally provides a method and apparatus foretching photomasks. One embodiment provides an apparatus for plasmaetching that includes a process chamber, a substrate support pedestal inthe process chamber, an RF power source for forming a plasma within thechamber, a shield disposed in the chamber above the pedestal and below aplasma forming region in the chamber, the shield configured to control adistribution of ionic and neutral species of the plasma, at least onegas inlet for providing a gas flow into the chamber, and a deflectorplate assembly disposed above the shield, the deflector plate assemblyconfigured to provide a predetermined gas flow pattern between the gasinlet and the shield.

The deflector plate may also be used in processing chambers without ashield. Another embodiment provides an apparatus for plasma etching thatincludes, for example, a process chamber, a substrate support pedestaldisposed in the process chamber, an RF power source for forming a plasmawithin the chamber, at least one gas inlet for providing a gas flow intothe chamber, and a deflector plate assembly disposed above the substratesupport pedestal and within a plasma forming region of the chamber, thedeflector plate assembly configured to provide a predetermined gas flowpattern between the gas inlet and the substrate support pedestal.

Another embodiment provides a method of etching a photomask in a processchamber that includes placing a photomask on a support pedestal,providing a shield above the support pedestal inside the chamber,introducing a process gas into the process chamber through at least oneinlet, providing a predetermined gas flow pattern between the gas inletand the shield by disposing a deflector plate assembly above the shield,forming a plasma from the process gas in a region above the shield, andetching the photomask with ions and neutral species passing through theshield.

Another embodiment provides a method of etching a photomask in a processchamber that includes providing a shield above a support pedestal insidethe chamber for controlling ions and neutral species passing through theshield, introducing a process gas into the process chamber through atleast one inlet at a first flow velocity, providing a deflector plateassembly above the shield, the deflector plate assembly configured toprovide a predetermined gas flow pattern between the gas inlet and theshield, placing a photomask on the support pedestal, forming a plasmafrom the process gas, etching a first photomask at the first flowvelocity, obtaining an etch rate profile based on the etched firstsubstrate, adjusting the process gas through the at least one inlet to asecond flow velocity based on the etch rate profile, and etching asecond photomask at the second flow velocity.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the presentinvention can be understood in detail, a more particular description ofthe invention, briefly summarized above, may be had by reference toembodiments, some of which are illustrated in the appended drawings. Itis to be noted, however, that the appended drawings illustrate onlytypical embodiments of this invention and are therefore not to beconsidered limiting of its scope, for the invention may admit to otherequally effective embodiments.

FIG. 1 is a schematic diagram of a plasma process chamber with adeflector plate assembly of the present invention;

FIG. 2 is a schematic diagram of a top view of one embodiment of a platein the deflector plate assembly of FIG. 1;

FIG. 3 is a schematic diagram of a perspective view of one embodiment ofa second plate in the deflector plate assembly of FIG. 1;

FIG. 4 is a flow chart of a method of etching a photomask according toone embodiment of the invention; and

FIGS. 5A-5D illustrate schematically different embodiments of anion-neutral shield that can be used in conjunction with the deflectorplate assembly.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures. It is contemplated that elements and features of oneembodiment may be beneficially incorporated in other embodiments withoutfurther recitation.

It is to be noted, however, that the appended drawings illustrate onlyexemplary embodiments of this invention and are therefore not to beconsidered limiting of its scope, for the invention may admit to otherequally effective embodiments.

DETAILED DESCRIPTION

The present invention provides a method and apparatus for etching of aphotomask substrate by providing improved control of the gas flowpattern and plasma uniformity. The apparatus includes a deflector plateassembly configured to control the radial and vertical components of agas flow provided in the processing chamber. The deflector plateassembly is disposed above the substrate. In one embodiment, a shield,also referred to as an ion-radical shield or ion-neutral shield, isdisposed between the deflector plate assembly and the substrate. Aplasma is formed in a quasi-remote, upper processing region of thechamber above the shield, which is configured for controlling thedistribution of charged and neutral species in the chamber duringprocessing.

In another embodiment, the deflector plate assembly is used to redirectthe flow of gases in the processing chamber. One embodiment of thedeflector plate assembly comprises a first plate having an aperture,whose location and dimension help define a primary direction of gas flowtowards the substrate (or the shield, if present). In anotherembodiment, the deflector plate assembly further comprises a secondplate disposed above the first plate. The second plate has a downwardlyprotruding portion that is substantially aligned with the aperture ofthe first plate. A gas flowing in a lateral direction, approximatelyparallel the first plate and the second plate, is deflected by thedownwardly protruding portion and redirected through the aperture of thefirst plate. By establishing a primary gas flow direction or pattern orincreasing the gas flow velocity in a predetermined region, thedeflector plate assembly can lead to an enhanced etch rate in apredetermined location, and thus, result in improved etch uniformity.

Examples of an ion-radical shield for use in a plasma etch chamber havebeen disclosed in U.S. patent application Ser. No. 10/880,754, entitled“METHOD AND APPARATUS FOR PHOTOMASK PLASMA ETCHING”, filed on Jun. 30,2004, by Kumar, et al., and in U.S. patent application Ser. No.11/554,495, entitled “METHOD AND APPARATUS FOR PHOTOMASK PLASMAETCHING”, filed concurrently herewith, by Kumar, et al., both of whichare hereby incorporated by reference in their entirety.

FIG. 1 depicts a schematic diagram of an etch reactor 100 having anion-radical shield 170. Suitable reactors that may be adapted for usewith the teachings disclosed herein include, for example, the DecoupledPlasma Source (DPS®) II reactor, or the Tetra™ I and Tetra™ II Photomasketch systems, all of which are available from Applied Materials, Inc. ofSanta Clara, Calif. The particular embodiment of the reactor 100 shownherein is provided for illustrative purposes and should not be used tolimit the scope of the invention. It is contemplated that the inventionmay be utilized in other processing systems, including those from othermanufacturers.

The reactor 100 generally comprises a process chamber 102 having asubstrate pedestal 124 within a conductive body (wall) 104, and acontroller 146. The chamber 102 has a substantially flat dielectricceiling or lid 108. Other modifications of the chamber 102 may haveother types of ceilings, e.g., a dome-shaped ceiling. An antenna 110 isdisposed above the ceiling 108 and comprises one or more inductive coilelements that may be selectively controlled (two co-axial elements 110 aand 110 b are shown in FIG. 1). The antenna 110 is coupled through afirst matching network 114 to a plasma power source 112, which istypically capable of producing up to about 3000 W at a tunable frequencyin a range from about 50 kHz to about 13.56 MHz.

Processing gases are provided into the chamber 102 through one or moreinlets 116 from a gas panel 120. The inlets 116 may be located on thelid 108 or wall 104 of the chamber 102. In the embodiment depicted inFIG. 1, the inlets 116 are positioned to induce a predominantly radialflow of gases entering the chamber 102, for example, through inlets 116formed in the walls 104 of the chamber 102.

The substrate pedestal (cathode) 124 is coupled through a secondmatching network 142 to a biasing power source 140. The biasing source140 generally is a source of up to about 500 W at a frequency ofapproximately 13.56 MHz that is capable of producing either continuousor pulsed power, Alternatively, the source 140 may be a DC or pulsed DCsource. In one embodiment, the substrate support pedestal 124 comprisesan electrostatic chuck 160, which has at least one clamping electrode132 and is controlled by a chuck power supply 166. In alternativeembodiments, the substrate pedestal 124 may comprise substrate retentionmechanisms such as a susceptor clamp ring, a mechanical chuck, and thelike.

A reticle adapter 182 is used to secure the substrate (e.g., mask orreticle) 122 onto the substrate support pedestal 124. The reticleadapter 182 generally includes a lower portion 184 that covers an uppersurface of the pedestal 124 (for example, the electrostatic chuck 160)and a top portion 186 having an opening 188 that is sized and shaped tohold the substrate 122. The opening 188 is generally substantiallycentered with respect to the pedestal 124. The adapter 182 is generallyformed from a single piece of etch resistant, high temperature resistantmaterial such as polyimide ceramic or quartz. An edge ring 126 may coverand/or secure the adapter 182 to the pedestal 124. A lift mechanism 138is used to lower or raise the adapter 182, and hence, the substrate 122,onto or off of the substrate support pedestal 124. Generally, the liftmechanism 162 comprises a plurality of lift pins 130 (one lift pin isshown) that travel through respective guide holes 136.

In operation, the temperature of the substrate 122 is controlled bystabilizing the temperature of the substrate pedestal 124. In oneembodiment, the substrate support pedestal 124 comprises a resistiveheater 144 and a heat sink 128. The resistive heater 144 generallycomprises at least one heating element 134 and is regulated by a heaterpower supply 168. A backside gas, e.g., helium (He), from a gas source156 is provided via a gas conduit 158 to channels that are formed in thepedestal surface under the substrate 122 to facilitate heat transferbetween the pedestal 124 and the substrate 122. During processing, thepedestal 124 may be heated by the resistive heater 144 to a steady-statetemperature, which in combination with the backside gas, facilitatesuniform heating of the substrate 122. Using such thermal control, thesubstrate 122 may be maintained at a temperature between about 0 and 350degrees Celsius (° C.).

An ion-radical shield 170 is disposed in the chamber 102 above thepedestal 124. The ion-radical shield 170 is electrically isolated fromthe chamber walls 104 and the pedestal 124 such that no ground path fromthe plate to ground is provided. One embodiment of the ion-radicalshield 170 comprises a substantially flat plate 172 and a plurality oflegs 176 supporting the plate 172. The plate 172, which may be made of avariety of materials compatible with process needs, comprises one ormore openings (apertures) 174 that define a desired open area in theplate 172. This open area controls the amount of ions that pass from aplasma formed In an upper process volume 178 of the process chamber 102to a lower process volume 180 located between the ion-radical shield 170and the substrate 122. The greater the open area, the more ions can passthrough the ion-radical shield 170. As such, the size of the apertures174 controls the ion density in volume 180, and the shield 170 serves asan ion filter. The plate 172 may also comprise a screen or a meshwherein the open area of the screen or mesh corresponds to the desiredopen area provided by apertures 174. Alternatively, a combination of aplate and screen or mesh may also be used.

During processing, a potential develops on the surface of the plate 172as a result of electron bombardment from the plasma. The potentialattracts ions from the plasma, effectively filtering them from theplasma, while allowing neutral species, e.g., radicals, to pass throughthe apertures 174 of the plate 172. Thus, by reducing the amount of ionsthrough the ion-radical shield 170, etching of the mask by neutralspecies or radicals can proceed in a more controlled manner. Thisreduces erosion of the resist as well as sputtering of the resist ontothe sidewalls of the patterned material layer, thus resulting inimproved etch bias and critical dimension uniformity.

Different combinations of materials and/or configurations are providedin various embodiments of the shield plate 172. In one embodiment, theplate 172 may be made of a materials having a dielectric constantgreater than about 4, including for example, ceramics such as alumina,yttria and K140 (a proprietary material available from Kyocera). Inanother embodiment, the plate 172 comprises two zones having at leastone characteristic that is different from each other. For example, theshield may comprise a number of zones with different configurationsincluding various geometries (e.g., sizes, shapes and open areas), andthe zones may be made of the same or different materials, or be adaptedto have different potential bias. By providing combinations of zoneconfigurations, materials and/or potential bias, the spatialdistribution of ions and neutrals in the plasma can be modified in alocalized manner, allowing customization of process characteristics suchas etch uniformity, or locally enhanced or reduced etch rates (e.g., totailor to different pattern densities in different parts of a mask), andso on. Such a multi-zone shield, for example, can be used for activecontrol of plasma species distribution, arid thus, allow for enhancedprocess control.

FIG. 5A illustrates one embodiment of a plate 172 having different zones172A, 172B, 172C and 172D, with at least two zones being made ofdifferent materials. Suitable materials include a variety of ceramics(e.g., alumina, yttria), anodized aluminum, quartz, materials withdielectric constant higher than about 4, e.g., K140 manufactured byKyocera. These zones can be provided in different geometricconfigurations or patterns, e.g., as wedges arranged in a circle (shownin FIGS. 5A), in concentric rings, in a grid or slice pattern, or othercombinations of different geometric shapes.

FIG. 5B illustrates another embodiment, where the plate 172 is madeprimarily of one material, but is divided into different zones orsegments, 172A, 172B, 172C and 172D, that are physically separated orelectrically isolated from each other. For example, zones of the samematerials may be separated by a gap 172G, or by a different material.These zones are configured so that each can be independently biased to adifferent potential. As shown in FIG. 5B, zones 172A and 172B connectedto respective power sources, e.g., 190A, 190B, for supplying a potentialbias, which can be independently controlled for each zone. Suchconnection may be provided through one of the support legs 176, as shownin FIG. 5C.

FIG. 5D shows yet another embodiment, where the plate 172 is made of onematerial with a potential bias applied across two locations, 172X and172Y, on the plate 172. The potential bias is applied by connectingvoltage sources 190C and 190D to the respective locations. In thisembodiment, there is no gap or physical separation between the two zonesof different potential bias around locations 172X and 172Y. Instead, apotential gradient is established on the plate 172 between locations172X and 172Y.

These various embodiments of the plate 172 can be used in combinationwith each other, e.g., a plate, whether made of a single material ordifferent materials, may comprise different zone configurations, or beprovided with different potential bias across the plate. The variouszones may also be configured to tailor to specific mask patterns so thatprocess characteristics can be customized to suit specific needs. Thus,if a mask has regions of different pattern densities or loading, thedesired etch rates for these regions may be different from each other.In that case, it is possible to configure the zones or segments on theshield plate 172 based on the specific mask patterns in order to achievethe desired etch result.

The apertures 174, which may vary in size, shape, spacing and geometricarrangement, may generally have dimensions ranging from 0.03 inches(0.07 cm) to about 3 inches (7.62 cm), and may be arranged to define anopen area within each zone of the plate 172 from about 2 percent toabout 90 percent. The size, shape and patterning of the apertures 174may be varied according to the desired ion density in the lower processvolume 180. For example, more apertures of small diameters in aparticular zone of the plate 172 may be used to increase the radical (orneutral) to ion density ratio in a corresponding region of the volume180. Alternatively, a number of larger apertures may be interspersedwith small apertures to increase the ion to radical (or neutral) densityratio in a corresponding region of the volume 180.

The height at which the ion-radical shield 170 is supported may vary tofurther control the etch process. The closer the ion-radical shield 170is located to the ceiling 108, the smaller the upper process volume 178,which tends to promote a more stable plasma. A faster etch rate may beobtained by locating the ion-radical shield 170 closer to the pedestal124 and, therefore, the substrate 122. Alternatively, a lower, but morecontrolled, etch rate may be obtained by locating the ion-radical shield170 farther from the pedestal 124. Controlling the etch rate byadjusting the height of the ion-radical shield 170 thus allows balancingfaster etch rates with improved critical dimension uniformity andreduced etch bias. It is contemplated that the ion-radical shield 170may be positioned at different heights in chambers having differentgeometries, for example, larger or smaller chambers.

The legs 176, which support the plate 172 in a spaced-apart relationshipwith respect to the substrate 122, are generally located around an outerperimeter of the pedestal 124 or the edge ring 126 and may be fabricatedof the same materials as the plate 172. In one embodiment, three legs176 are used to support the ion-radical shield 170. Although the legs176 generally maintain the plate 172 in a substantially parallelorientation relative to the substrate 122 or pedestal 124, an angledorientation may also be used by having legs 176 of varied lengths. Thelegs 176 may be secured to the plate 172 by a variety of fasteningmethods, and may be supported on the pedestal 124, adapter 182, or theedge ring 126.

Alternatively, the plate 172 may be supported above the pedestal 124 byother means such as by using a bracket (not shown) attached to the wall104 or other structure within the process chamber 102. In thesesituations, the plate 172 is generally insulated from any ground pathsuch as the ground 106.

According to one embodiment of the present invention, a deflector plateassembly 200 is provided above the plate 172. In other embodiments wherethe plate 172 is absent, the deflector plate assembly 200 is disposedabove the reticle adapter 182 and/or edge ring 126. In one embodiment,the deflector plate assembly 200 comprises a first plate 210 maintainedin a spaced-apart relationship to the plate 172 by a first supportassembly 202. The first plate 210 can be fabricated from a variety ofmaterials compatible with the processes, e.g., ceramic, quartz, oranodized aluminum. As shown in a schematic cross-section view in FIG. 1,the first plate 210 has an aperture 215 that changes the primary gasflow direction for the plasma gases entering the chamber 102 from gasinlets 116 towards the plate 172. In one embodiment, the aperture 215 islocated at the center of the first plate 210, which is also aligned withthe center of the shield plate 172. In other embodiments, the aperture215 may be disposed at other locations on the first plate 210 in orderto provide desired gas flow patterns to suit specific processing needs.Furthermore, additional apertures may be provided at various locationsof the first plate 210, if desired. For example, apertures havingsmaller diameters compared to aperture 215 may be used to provide finetuning of the gas flow pattern.

The first support assembly 202 may comprise one or more support members,e.g., a plurality of elongated members or legs, coupling the first plate210 to the shield plate 172. The legs may be attached to the shieldplate 172 and the first plate 210 by a variety of conventional means,including screws, bolts, and so on. FIG. 2 is a schematic diagram of atop view of one embodiment of the first plate 210. In one embodiment,three legs are used to attach the first plate 210 to the shield plate172, e.g., by threading the legs to mounting holes 212, 213, 214 on thefirst plate 210. The vertical distance between the first plate 210 andthe shield plate 172 may vary, depending on factors such as the chamberdimension, pumping configuration, gas flow requirements and specificprocess needs. In one embodiment, the first plate 210 is located at adistance of about 2 to 3 inches above the shield plate 172. In otherembodiments, the separation distance may range from about 5 inches toabout 6 inches.

In another embodiment, the deflector plate assembly 200 furthercomprises a second plate 220 disposed above the first plate 210. Asshown in FIG. 1, the second (or top) plate 220 is supported on the first(or bottom) plate 210 by a second support assembly 204. The top plate220 has a downwardly protruding portion 225 disposed proximate to theaperture 215 of the bottom plate 210. In one embodiment, the downwardlyprotruding portion 225 is located at the center of the top plate 220,and furthermore, is aligned laterally relative to the aperture 215,which has a diameter of about 50.8 mm (2 inches).

FIG. 3 is a schematic illustration of a perspective bottom view of thetop plate 220, showing the downwardly protruding portion 225 near thecenter. In this embodiment, the top plate 220 has three threaded holes222, 224, 226 for coupling to respective support members of the secondsupport assembly 204, which are attached at the other ends to the bottomplate 210 at mounting holes 216, 217, 218 (in FIG. 2). The downwardlyprotruding portion 225 generally has a cross-sectional shape similar tothat of the aperture 215, e.g., a conical or truncated conical shape inthe embodiment of FIG. 3. The protruding portion 225 preferably has ataper towards the center, e.g., having one end (or the base) 227 at theplane of the plate 220 wider than a far or distal end 229, i.e.,dimension d₁ being larger than d₂.

In one embodiment, the top plate 220 and the bottom plate 210 isseparated by a distance of about 38.1 to 50.8 mm (1.5 to 2 inches), andthe aperture 215 is a circle with a diameter of about 50.8 mm (2inches). For this configuration, simulation results show that arelatively focused vertical gas flow towards the shield and aperpendicular flow to the photomask substrate surface can be establishedwith a side injection gas velocity ranging from about 5 m/s to about 20m/s, although other velocities may also be used. One of the criteria forselecting certain gas flow velocities and deflector plate assemblydimensions is that a relatively focused vertical gas flow be maintainedperpendicular to the ion radical shield. In other embodiments, theseparation distance may range from about 25.4 to 76.2 mm (1 to 3inches), and the aperture diameter may range from about 25.4 to 76.2 mm(1 to 3 inches). In general, the distances between the top plate 220,the bottom plate 210, and the shield plate 172, the degree of taper,shape or dimension of the protruding portion 225, as well as the shape,location and dimension of the aperture 215, may vary according tospecific design and application needs, taking into considerationsvarious factors such as the chamber dimension, pumping configuration,gas flow velocities, and so on. Aside from achieving certain desiredetch rate or uniformity results, the design parameters are selected toprovide a process with relatively wide margins.

Prior to plasma etching, one or more process gases are provided to theprocess chamber 102 from a gas panel 120, e.g., through one or moreinlets 116 (e.g., openings, injectors, nozzles, and the like) locatedabove the substrate pedestal 124. In the embodiment of FIG. 1, the gasinlets 116 are disposed above the bottom plate 210 of the deflectorplate assembly 200. As shown In FIG. 1, the process gases are providedto the inlets 116 using an annular gas channel 118, which may be formedin the wall 104 or in gas rings (as shown) that are coupled to the wall104. By appropriate choice of the gas flow velocities, the location ofthe deflector plate assembly 200, and the size of aperture 215, theprocess gases can be directed to flow primarily towards the center ofthe chamber 102, e.g., along the direction indicated by arrows 250.Thus, the process gases flow in a lateral direction above the bottomplate 210, e.g., radially inwards from the side gas inlets 116, anddownwards through the aperture 215 of the bottom plate 210 towards theshield plate 172. In alternative embodiments in which only the firstplate 210 is used, the gas inlets 116 may also be provided in otherlocations of the chamber 102, e.g., at the lid 108 or be centrallylocated on the lid 108.

When the top plate 220 is used, the gas inlets 116 are disposed at avertical location at or below the top plate 220. In this embodiment, thegas flow between the top plate 220 and the bottom plate 210, e.g., in aradially inward direction, is deflected or re-directed by the downwardlyprotruding portion 225 through aperture 215. By adjusting the radialvelocities of gases entering the chamber 102, the positions of thedownwardly protruding portion 225 and the aperture 215, as well as thevertical locations of the top and bottom plates 220, 210, the spatial orlateral distribution of ions and neutral species passing through shield170 can be controlled, which in turn, allows the etch rate profile to betuned. Although the aperture 215 is centrally located on the bottomplate 210 in this illustrative embodiment, it can also be disposed atother locations, or be provided with different shapes and dimensions, inorder to establish desired flow patterns that are suitable for otherapplication needs. During an etch process, the process gases are ignitedinto a plasma by applying power from the plasma source 112 to theantenna 110.

The pressure in the chamber 102 is controlled using a throttle valve 162and a vacuum pump 164. The temperature of the wall 104 may be controlledusing liquid-containing conduits (not shown) that run through the wall104. Typically, the chamber wall 104 is formed from a metal (e.g.,aluminum, stainless steel, among others) and is coupled to an electricalground 106. The process chamber 102 also comprises conventional systemsfor process control, internal diagnostic, end point detection, and thelike. Such systems are collectively shown as support systems 154.

The controller 146 comprises a central processing unit (CPU) 150, amemory 148, and support circuits 152 for the CPU 150 and facilitatescontrol of the components of the process chamber 102 and, as such, ofthe etch process, as discussed below in further detail. The controller146 may be one of any form of general-purpose computer processor thatcan be used in an industrial setting for controlling various chambersand sub-processors. The memory, or computer-readable medium, of the CPU150 may be one or more of readily available memory such as random accessmemory (RAM), read only memory (ROM), floppy disk, hard disk, or anyother form of digital storage, local or remote. The support circuits 152are coupled to the CPU 150 for supporting the processor in aconventional manner. These circuits include cache, power supplies, clockcircuits, input/output circuitry and subsystems, and the like. Theinventive method is generally stored in the memory 148 as a softwareroutine. Alternatively, such software routine may also be stored and/orexecuted by a second CPU (not shown) that is remotely located from thehardware being controlled by the CPU 150.

FIG. 4 illustrates a method 400 that can be used for etching a photomasksubstrate in an etch chamber incorporating the deflector plate assemblyof the present invention. The method 400 begins at step 402 in which aprocess chamber is provided with a deflector plate assembly and anion-neutral shield above a support pedestal. The deflector plateassembly has at least one aperture located above the shield.

At step 404, a substrate is placed on the support pedestal. Typicalsubstrates generally comprise an optically transparent silicon basedmaterial, such as quartz (i.e., silicon dioxide, SiO₂), having an opaquelight-shielding layer of metal disposed on the surface of the quartz.Typical metals used in a photomask include chromium or chromiumoxynitride. The substrate may also include a layer of silicon nitride(SiN) doped with molybdenum (Mo) interposed between the quartz andchromium.

At step 406, at least one process gas is introduced into the processchamber through a gas inlet located above the aperture of the deflectorplate assembly. The direction of the process gas flow towards the shieldis partly defined by the aperture of the deflector plate assembly andthe location of the gas inlets. For embodiments where gas inlets areprovided around the perimeter region of the chamber, a gas flow isestablished in a radially inward direction towards the aperture, e.g.,by providing an appropriate flow velocity. A second plate having adownwardly protruding portion is provided above the first plate forre-directing the gas flow downwards towards the aperture.

Exemplary process gases may include oxygen (O₂) or an oxygen-containinggas, such as carbon monoxide (CO), and/or a halogen-containing gas, suchas a chlorine-containing gas for etching the metal layer. The processinggas may further include an inert gas or another oxygen-containing gas.Carbon monoxide is advantageously used to form passivating polymerdeposits on the surfaces, particularly the sidewalls, of openings andpatterns formed in a patterned resist material and etched metal layers.Chlorine-containing gases are selected from the group of chlorine (Cl₂),silicon tetrachloride (SiCl₄), boron trichloride (BCl₃), andcombinations thereof, and are used to supply reactive radicals to etchthe metal layer. In other embodiments such as those for etching quartzor MoSi, the process gases may comprise a fluorine-containing gas, e.g.,trifluoromethane (CHF₃), tetrafluoromethane (CF₄), among others.

At step 408, a plasma is formed from the process gas in a process volumeabove the ion-radical shield, for example, by applying RF power from aplasma power source to an antenna. Ions and neutral species pass throughthe ion-radical shield according to a distribution pattern resultingfrom a combination of the process gas flow direction (as defined by thedeflector plate assembly) and the potentials across the ion-radicalshield. The substrate is etched by the ions and neutral species in thelower process volume.

The method and apparatus of the present invention can be usedadvantageously, for example, in an etch process that otherwise exhibitsa radial non-uniformity such as one having a slower etch rate at thecenter compared to the edge. By establishing a gas flow direction orpattern or increasing the gas flow velocity in a predetermined region,e.g., the center region, the deflector plate assembly can lead to anenhanced etch rate in a corresponding region of the photomask, and thus,result in improved etch uniformity. For a given deflector plate assemblyconfiguration within a chamber, the flow velocities of one or moreprocess gases in various applications can also be adjusted to achievedesired etch profile or process results.

While the foregoing is directed to embodiments of the present invention,other and further embodiments of the invention may be devised withoutdeparting from the basic scope thereof, and the scope thereof Isdetermined by the claims that follow.

1. An apparatus for plasma etching, comprising: a process chamber; asubstrate support pedestal disposed in the process chamber; an RF powersource for forming a plasma within the chamber; a shield disposed in thechamber above the pedestal and below a plasma forming region in thechamber, the shield configured to control a distribution of ionic andneutral species of the plasma, wherein the shield comprising two zoneshaving at least one characteristic different from each other, the atleast one characteristic being one of material or potential bias; atleast one gas inlet disposed radially outward of the shield forproviding a gas flow into the chamber in a direction parallel to theshield; and a deflector plate assembly disposed above the shield, thedeflector plate assembly configured to provide a predetermined gas flowpattern between the gas inlet and the shield, wherein the deflectorplate assembly comprises a first plate having an aperture.
 2. Theapparatus of claim 1, wherein the at least one gas inlet is disposedabove the first plate.
 3. The apparatus of claim 1, wherein the apertureis located at a center of the first plate and substantially aligned witha center of the shield.
 4. The apparatus for claim 1, wherein theaperture is circular and has a diameter between about 25.4 mm to about76.2 mm.
 5. The apparatus of claim 1, wherein the deflector plateassembly is fabricated from at least one of ceramic, quartz, or anodizedaluminum.
 6. The apparatus of claim 1, wherein the support pedestal isconfigured for supporting a photomask.
 7. The apparatus of claim 1,wherein the first plate of the deflector plate assembly is attached tothe shield by a support assembly.
 8. The apparatus of claim 7, whereinthe first plate is supported in a substantially parallel, spaced apartrelation with respect to the shield.
 9. The apparatus of claim 1,wherein one of the characteristic is material.
 10. The apparatus ofclaim 9, wherein each of the two zones comprises a material with adielectric constant different from each other, the material beingselected from the group consisting of anodized aluminum, ceramics,alumina, yttria, and materials having a dielectric constant higher thanabout
 4. 11. The apparatus of claim 1, wherein the deflector plateassembly further comprises a second plate disposed above the firstplate, the second plate having a downwardly protruding portion disposedabove the aperture.
 12. The apparatus of claim 11, wherein thedownwardly protruding portion is substantially aligned with the apertureof the first plate.
 13. The apparatus of claim 11, wherein thedownwardly protruding portion has a first end at a plane of the secondplate and a distal end, the first end having a lateral dimension that islarger than a lateral dimension at the distal end.
 14. The apparatus ofclaim 13, wherein the lateral dimension at the base of the protrudingportion is larger than a diameter of the aperture of the first plate.15. An apparatus for plasma etching, comprising: a process chamber; asubstrate support pedestal disposed in the process chamber; an RF powersource for forming a plasma within the chamber; a shield disposed in thechamber above the pedestal and below a plasma forming region in thechamber, the shield configured to control a distribution of ionic andneutral species of the plasma, wherein the shield comprises two zones;at least one gas inlet for providing a gas flow into the chamber; and adeflector plate assembly disposed above the shield, the deflector plateassembly configured to provide a predetermined gas flow pattern betweenthe gas inlet and the shield, wherein the two zones of the shield haverespective potential bias different from each other.
 16. An apparatusfor plasma etching, comprising: a process chamber; a substrate supportpedestal disposed in the process chamber; an RF power source for forminga plasma within the chamber; at least one gas inlet for providing a gasflow into the chamber; a shield disposed in the chamber above thesubstrate support pedestal and below a plasma forming region in thechamber, the shield comprising two zones having respective potentialbias different from each other; and a deflector plate assembly disposedabove the substrate support pedestal and within the plasma formingregion of the chamber, the deflector plate assembly configured tocontrol radial to vertical components of a gas flow pattern between thegas inlet and the substrate support pedestal in response to changes ingas velocity.
 17. The apparatus of claim 16, wherein the at least onegas inlet is disposed in a sidewall of the process chamber for producinga radial gas flow.
 18. The apparatus of claim 16, wherein the deflectorplate assembly comprises a first plate having an aperture.
 19. Theapparatus of claim 18, wherein the aperture is located in a centralregion of the first plate.